Image sensors having a matrix-type configuration of light-sensitive elements, i.e., pixels, are designed in particular using CMOS or CCD technology.
Image sensors may be used for various applications. One field of application is the use for an image processing system in a driver assistance system. Depending on the function of such a driver assistance system, it is necessary to image the entire color space of an object to be recorded, for example, the surroundings of a vehicle, with good color fidelity or to subdivide objects into approximate color classes. So-called three-chip cameras, having one spectral channel each for red, green and blue are used for electronic image recording with high color fidelity. A camera includes, in addition to the image sensor, optical elements in particular, such as lenses, polarizers or filters. In addition, it is known that cameras having image sensors may be used, in which a color filter, typically a red, green or blue filter, is situated in front of the individual light-sensitive elements. This filter configuration is known as a “color mosaic filter.” The mosaic configuration depends on the intended use of the camera. One of the most conventional filter patterns is the Bayer pattern, which allows good color separation in the entire CIE (International Commission on Illumination) color space.
In semiconductor-based image sensors, thin on-chip mosaic filter layers made of organic materials which selectively filter light spectrally, depending on its composition, are typically used for the color separation. The mosaic filter layers are thus applied directly to the light-sensitive elements of the image sensor. The filter characteristic of such filters is usually transparent over a large spectral range, in particular in the infrared spectral range. For example, to be able to perform a color separation effectively, an additional filter unit is necessary for performing a damping of the infrared radiation, for example.
Additional filters are usually designed extensively to be a separate unit detached from the image sensor or to be an applied layer on optical elements. DE 10 2004 001 556 A1, for example, describes a camera having an image sensor, a separate filter unit being situated at a distance in front of a partial area of the image sensor. The filter unit is used to dampen the low beam light range, so that the sensitivity of the image sensor is preserved in the near infrared range.